One means of detoxication for compounds foreign to the organism is their conversion to a mercapturic acid. Compounds bearing a highly electrophilic carbon atom react with glutathione to form a thioether of glutathione that is subsequently shorn of glycine and glutamic acid, yielding a thioether of cysteine. This is a key intermediate which can go on to form a mercapturic acid, i.e., the N-acetyl derivative of the cysteine thioether, as catalyzed by cysteine S-conjugate N-acetyltransferase in the presence of acetyl-CoA. However, a shunt mechanism exists in which cysteine conjugate beta-lyase catalyzes the formation of the appropriate thiol, pyruvate and ammonia from the cysteine thioether; the thiol is detoxified by action of thiol S-methyltransferase. The three enzymes are under study.